This issue tracks the work needed for the wildcard variables feature to be supported in Dart2JS.

We may need to do some additional work to support multiple wildcard parameters in functions.

class A {
  int add(int a, int b) => 3;
}

class C implements A {
  int add(int _, int _) => 3;
}

cc. @sigmundch Feel free to tag or reassign as you see fit.
I'd also appreciate more details so we don't lose that context.